Male Sprague--Dawley KC1 depleted rats were tube fed sodium chloride for three days. Citrate excretion decreased to 10 percent of control values, renal cortical citrate content fell by 50 percent, and urinary ammonia excretion increased three to fourfold. Although plasma bicarbonate concentration fell blood pH values remained significantly alkalotic. Urinary pH meanwhile rose sightly and plasma chloride concentration rose significantly. However, 14CO2 production by renal cortical slices incubated with C14-1,5 citrate was unaffected by varying the chloride concentration of the incubation media. KC1 depleted rate were then volume expanded with intravenous mannitol. This resulted in a decrease in plasma bicarbonate, maintenance of blood pH at alkalotic levels, and a rise in urinary pH. Glomerular filtration rate also rose. Compared to control non-expanded periods and to rats net volume expanded but maintained on low volume dextrose sinfusion, mannitol expanded rats decreased urinary citrate excretion, decreased renal cortical citrate content, and increased urinary ammonia excretion. The changes in renal citrate and ammonia metabolism were essentially identical to those seen after sodium chloride feeding but in this situation serum chloride fell indicating the effect on renal metabolism is due to volume expansion, not to altered serum chloride concentration.